Method for the manufacture of contact lenses using microwave energy

ABSTRACT

The invention concerns a method for manufacturing a contact lens, through molding within water-tight molds. The polymerization of lenses is insured by arranging a number of molds within one or several sealed metallic chambers (9) constituting a resonant cavity of a unique mode for an ultra high frequency wave; these molds are positioned in an area of the cavity where the electromagnetic field approximately of ultra high frequency waves is homogeneous, and are distributed so that the amounts of basic composition to be polymerized act as a load fitted to the inside of said cavity.

The invention concerns an improved method of manufacture, throughmolding, of a contact lens constituting a finished product having theoptical qualities required to be placed in contact with an eye and toinsure the desired corrections of vision. It extends to a new apparatusfor the use of this method.

The French patent application No. 80,04751 published Sept. 4, 1981 underU.S. Pat. No. 2,477,059 described a lens manufacturing process in whichthe lenses are made in a water-tight mold, under the proper conditionsto directly lend them final form with the appropriate opticalproperties, without an added machining operation.

The present invention proposes improvements of this method with a viewto increasing the quality of the lenses obtained.

A further objective of the invention is to reduce the neededmanufacturing time and consumption of energy.

A further objective is to permit manufacture of very thin lenses, whilelending these latter the appropriate optical qualities.

To that end, the method's aims consist essentially:

in constructing water-tight molds, reproducing in hollows the shape oflenses to be obtained and composed of a transparent or barely absorbentmaterial with respect to ultra high frequency electromagnetic waves,said molds being constructed so as to possess a thermic inertia muchhigher than the portion of basic composition need to make a lens:

in preparing a basic composition from one or several monomers withdouble polymerizable bonds, having an absorbent quality with respect toultra high frequency waves;

in insuring polymerization of the composition within the sealed molds,through irradiation by means of ultra high frequency waves.

According to the present invention, the polymerization operation iscarried out by arranging several molds, each containing an amount ofbasic composition, within at least one sealed metallic chamberconstituting a resonant cavity of a unique mode for the frequency of theultra high frequency waves used, said molds being positioned in an areaof the cavity where the electromagnetic field is approximatelyhomogeneous and being distributed so that the amounts of basiccomposition contained in said molds act as a load fitted to the insideof said resonant cavity.

The molds especially used are two-part molds which fit tightly into oneanother.

One preferably uses a chamber possessing ring geometry, that is, acylindrical chamber, constituting a resonant cavity according to theTransverse Magnetic Mode (TM 010); this chamber is excited by ultra highfrequency radiation means suitable to promote this mode of resonance, inparticular a radiating antenna extending the length of chamber's axis ora radiating iris located on its median transverse plane, so that theelectromagnetic field created in the cavity is composed of an electricalfield whose lines of force are appreciably straight lines parallel tochamber's rotational axis, and of a magnetic field whose lines of forceare appreciably circles centered upon this axis.

It should be noted that other modes of excitation are anticipated ifneed be, especially by inductive loops perpendicular to the planes ofthe magnetic field's lines of force. The mode of resonance may be yetdifferent, constituted especially by the TM 110 mode, where theelectrical field's lines of force are appreciably straight linesparallel to the rotational axis and the magnetic field's lines of forceare curves, located in planes perpendicular to the axis and possessing aplane of symmetry passing throu.hg this axis.

In accordance with a preferred mode of use, the molds are arranged instacks, superposed upon one another to form one or several columnssituated the length of or around the chamber's rotational axis, in areaswhere the electromagnetic field is at a maximum and appreciablyhomogeneous.

Experiments have shown that such a method insures an identical treatmentof all the lenses contained in the cavity, without sudden or periodicvariation, and allows to insure an energy-transfer under optimalconditions to obtain lenses of remarkable optical quality, without riskof deformity or separation of matter in the polymerization process.

In accordance with another characteristic of the present invention, onepreferably provides for ventilation of the chamber in order to avoid atemperature gradient within this latter. For the majority ofpolymerizable substances used, the chamber will be supplied with ultrahigh frequency waves so that the average energy density within thislatter may be comprised between temperature 10⁻² and 50×10⁻² cm³ /watts.

Under these conditions, the temperature around the molds isapproximately homogeneous and below apprioximately 40° C.

The basic compositions used to make lenses are constituted in particularby a monomer or a mixture of monomers having a high-volume molecule,from the following group: hydroxy-ethyl methacrylate, hydroxy-propylmethacrylate, hydroxy-ethyl acrylate, ethylene glycol dimethacrylate,vinyl pyrrolidone N, methyl methacrylate, methacrylic acid.

Going by experimental observations, the results obtained are improved inthe majority of cases by mixing with said basic composition initiatorconstituted in particular by azobis iso butyro nitril or hydro-peroxideor a peroxide, in weight proportion comprised between approximately0.04% and 0.15%.

The invention extends to an apparatus for contact lens manufactureallowing to put to use the disclosed method; this apparatus essentiallycomprises generation means for ultra high frequency waves ofpredetermined frequency, a sealed metallic chamber, suitable to form aresonant cavity of a unique mode for the frequency of said waves,radiation reans coupling the wave generation means and said resonantcavity, and positioning means for several molds in said cavity, designedto allow arrangement of said molds in an appreciably homogeneouselectromagnetic field area of said cavity.

The chamber of said apparatus may be especially of cylindrical form,with an inside diameter D such that:

    D=2.29.10.sup.4 /f±1% in the case of the TM 010 mode

    D=3.65.10.sup.4 /f±1% in the case of the TM 110 mode

where D is expressed in millimeters and where f is the wave frequencyexpressed in megahertz. (The frequency used being generally anindustrial frequency: 2,450 Mhz, 915 Mhz, 434 Mhz . . . )

Moreover, the invention's apparatus is advantageously equipped withventilation means fit to insure an external air-flow around the chamber,or even a blower system within this latter, combined with an air exhaustopening.

The invention's apparatus may include one chamber only or else severalconnected chambers so as to be submitted to an appreciably identicalenergy distribution.

The invention having been presented in its general form, othercharacteristics, goals, and advantages of this latter will emerge fromthe following description, which refers to the drawings herewith,furnished on non-restrictive grounds to illustrate the invention; onthese drawings:

FIG. 1 is a diagrammatic view of a lens manufacturing apparatusaccording to the present invention;

FIGS. 2 and 3 are respectively transverse cross-sectional view AA andaxial cross-sectional view BB, of a chamber equipping said apparatus;

FIGS. 4 and 5 are perspective views, representing other ways to effectthe positioning of molds within the chamber;

FIGS. 6 and 7 diagram two modes of realization of ventilation meansconnected to said chamber;

FIGS. 8 and 9 partially diagram other ways to construct the apparatus,equipped with several chambers;

FIG. 10 diagrams one other way to construct the apparatus;

FIGS. 11 and 12 are axial cross-sectional views of two variations of theapparatus diagrammed in FIG. 10.

The apparatus shown as an example in FIGS. 1, 2, and 3 is intended foruse in the molding manufacture of hydrophilic (or soft) contact lenseshaving, right after molding, all the required geometrical, mechanical,and optical characteristics without need for machining or otherfinishing operations.

To this end, one uses molds (shown superposed as part 1 of FIG. 3),which are each composed of two parts interlocking in a water-tightmanner, to delineate a closed molding volume in which is placed anamount of basic composition designated to form a lens. Each part of themold is made of material transparent with respect to ultra highfrequency waves, especially of pure uncharged polypropylene,polyethylene, and polymethylpentene, and presents a volume and weightmuch greater than the portion of basic composition contained in themold.

The invention aims toward an apparatus designed to carry outpolymerization of several lenses under suitable conditions to obtain theperfect geometric and optical qualities of these latter. It includes amagnetron 2 connected to an electrical source unit 3, which generatesultra high frequency waves of determined frequency in a waveguide 4 ofrectangular form suitable to allow propagation of the fundamental modeat the selected frequency.

Interposed the length of waveguide 4 are a circulator 5 allowing todivert the reflected wave toward an auxiliary load in order to protectthe magnetron in case of a considerable increase in the stationary waverelation, a bicoupler 6 connected to a milliwattmeter 7 to control thevalue of this stationary wave relation and an adjustable E/H adapter 8,allowing to vary this relation in order to adjust it to a value near 1.

To that end, this adapter includes two variable short circuits, formedby metallic pistons which can be moved within the two lateral portionsof the waveguide (one parallel to the electrical field, the other to themagnetic field).

At one end of guide 4 is connected a metallic chamber of cylindricalform 9, constituting a resonant cavity in accordance with the TM 010mode.

This chamber 9, shown in a cross-sectional view in FIG. 3, is brass andis sealed at each end by a brass disk, the upper disk being removable.For a wavelength equal to 2,450 megahertz which is used in the followingexamples, its inside diameter D is substantially equal to 93.7 mm.

The chamber 9 is connected to guide 4 on which it is fastened by theinterposition of a metallic axial antenna 10 which extends through apart of chamber's height (between about 2/3 to 3/4 of this height). Thisantenna passes through an aperture cut in the chamber's lower disk topenetrate into the waveguide 4 through another aperture cut in thislatter. At its end the antenna 10 is fastened to a crossbar 11 which isset in the guide 4 between the side walls of this latter.

In this instance, the antenna 10 is held by a metallic piece 12 solderedto the cross-bar 11 and guided by a polytetrafluoroethylene O-ring atthe level of the guide's aperture; the end of antenna 10 is screwed intoan eye-holes tapped in piece 12.

The molds 1 are arranged as shown in FIGS. 2 and 3, around antenna 10,superposed within eight columns. They are held in this position bytubular guides such as 13 or 14, made of a dielectric materialtransparent or barely absorbent with respect to ultra high frequencywaves, especially of polytetrafluoroethylene or silicone. These guidespossess an extra inside thickness at their base to form a stop for thelower molds. The inside diameter of these guides is slightly greaterthan the molds' outside diameter in order to contain these latter.

The tubular guides 13 and 14 are positioned in chamber 9, parallel tothe axis of this latter, by two retainer disks such as 15 which areinserted edgewise against the inside circular chamber wall; these disksare made of the same material as guides 13 and 14 and include eightholes for passage of same. Guides 13 and 14 are hence removable and maybe taken out for placement of molds within them and then inserted in thechamber in the appropriate, always identical positions thanks toretainer disks 15.

As shown in FIGS. 2 and 3, four central tubular guides such as 13 arearranged in the immediate vicinity of antenna 10 to extend almost to thechamber's height, while four peripheral guides such as 14 are arrangedat the immediate circumference of central guides 13 to extend over afraction of the chamber's height (at middle zone level).

The molds contained in these guides are thus arranged in superposedcolumns: four taller columns, located in the immediate vicinity of theantenna and diametrically opposed two-by-two, and four additionalshorter ones arranged in the spaces separating the first around theirexterior circumference, as shown in FIG. 2. The usable central volumeoccupied by these columns of molds represents a fraction of the totalchamber volume.

Experiments have shown that this fraction could be on the order of onefourth of the total volume: the electrical field whose lines of forceare straight lines parallel to the antenna and the magnetic field whoselines of force are concentric circles around these lines, areappreciably homogeneous in this volume, except in the upper and lowerareas located above and below guides 14 (which explains that same aredesigned shorter so as not to extend into these areas).

Moreover, it has been determined in certain applications of the presentmethod, that it is useful to provide for auxiliary dielectric loads inplace of certain molds. These loads, made of an absorbent material withrespect to the ultra high frequency waves, may be constituted by moldscontaining portions of basic composition, but the lenses obtained willafterwards be discarded by reason of their inferior quality compared tothe others. These loads are useful to increase the homogeneity of theelectromagnetic field at the level of the usable molds, whilefacilitating the adaptation of the unit to the load contained in thecavity in order to obtain a high energy yield (capable of reaching 90%).Tests have shown that these loads should be generally located at thebase of guides 13 (taller guides).

FIG. 4 presents another way to make a tubular guide; in this mode ofconstruction the guide is latticed and the guiding of molds is insuredby four uprights 16, braced by circular parts 17. It should be notedthat one may, if need be, plan to use interlocking molds, so as to allowsimplification or even complete suppression of the guides.

FIG. 5 presents (on a smaller scale) another realization of positioningmeans for the molds. The eight aforementioned guides are replaced by asingle column 18 guide of an analogous material, transparent withrespect to ultra high frequency waves), which possess transverseeye-holes such as 19, allowing one to place and secure the molds. Theselatter are then each superposed in a transverse position (FIG. 5represents one of the molds in place). Column 18 is arranged aspreviously around the antenna which is placed in an axial aperture 20 ofsaid column.

Moreover, with a view to avoiding the appearance of a temperaturegradient due to an overheating and a convection within chamber 9,ventilation means allowing to cool the upper part of said chamber arepreferably connected to the apparatus.

This ventilation may be insured by an exterior fan 21 (FIG. 6) axiallyarranged above chamber 9. This arrangement suffices to suitably limitthe temperature gradient in cases where the load contained in thechamber is relatively small.

In the opposite case, one preferably anticipates a blower fit to createan air-flow within the chamber (FIG. 7). This flow is brought in throughan axial aperture 22 in the upper disk, is guided by a central column 23(of material transparent with respect to the ultra high frequency waves)which surrounds the antenna from one end of the chamber to the other,penetrated by holes cut in the upper part of column 23; exhaust openings24 are provided in the chamber's cylindrical wall for the evacuation ofair.

The apparatus may be equipped with a single chamber 9 as preferablydescribed or with several identical chambers as shown in FIGS. 8 and 9.

The apparatus shown in FIG. 8 is equipped with two chambers connected bythe same cross-bar at the end of the waveguide, these chambers beingarranged symmetrically in relation to one another.

The apparatus shown in FIG. 9 is equipped with two chambers, connectedby two cross-bars located in a segment of the waveguide thattransversally extends the path waveguide. The two transverse bars arespread apart at a distance equal to the length of the guided wave. It ispossible to put four chambers in place by combining the pairing-off ofFIG. 8 to that of FIG. 9.

If need be, other pairings may be provided to set up a greater number ofchambers and submit them to the same energy distribution.

Moreover, FIGS. 10, 11, and 12 diagram another mode of construction inwhich the chamber is connected to the end of waveguide 4 by a radiatingiris 25. This iris is symmetrical in relation to the chamber'stransverse median plane and is formed by a slit cut in the cylindricalwall of this latter.

For a chamber having the already indicated dimensions, the diameter ofthis iris is 34 mm and its expanded diameter from 50 to 60 mm, dependingupon the load and node of use.

Furthermore, the chamber is perforated at the center of its upper andlower cylindrical walls by two apertures rimmed by guide flanges 26 and27.

Molds of the type already mentioned are contained in a tubular centralpolytetrafluoroethylene guide 28 which runs through the chamber thelength of its axis.

In the case of FIG. 11, the molds are motionless during processing andstopped in guide 28 at the center of the chamber by a ring 29 fastenedin said column. After the processing, the tubular guide 28 is withdrawnfrom the chamber to replace the molds.

In the case of FIG. 12, the upper part of tubular guide 30 extends to aloader 31 composed of a tube containing molds and includes at its lowerend an evacuation conduit 32 which deposits the molds on a conveyor belt33. The molds thus run through the chamber, and processing is effectedcontinuously. The conveyor belt speed is adjusted so as to leave moldsthe appropriate time within the usable central chamber volume.

Examples 1, 2, and 3 provided below were put to use by means of anapparatus with a chamber of the type represented in FIGS. 1, 2 and 3,with external ventilation of the type shown in FIG. 6. Examples 4 and 5were put to use respectively in an apparatus such as the one shown inFIG. 11 and in an apparatus such as the one shown in FIG. 12. In eachinstance, the wavelength used was 2,450 megahertz and the chamber heightwas 294 mm.

EXAMPLE 1

Basic composition placed in each sealed mold:

    ______________________________________                                        Basic composition placed in each sealed mold:                                 ______________________________________                                        Hydroxy ethyl methacrylate (Hema)                                                                    72.14%  (by weight)                                    Hydroxy propyl methacrylate (Hpma)                                                                   23.73%                                                 Hydroxy ethyl acrylate (Hea)                                                                         2.00%                                                  Ethylene glycol dimethacrylate (Egdma)                                                               0.05%                                                  Polyvinyl pyrrolidone (PVP)                                                                          2.00%                                                  Azobis iso butyro nitril (AIBN)                                                                      0.08%                                                  ______________________________________                                    

Weight of portion within each mold=0.05 g

Number of usable molds placed in chamber=36

Clean weight of each mold: 1.30 g

Number of auxiliary loads formed by molds containing lost portions: 12

Arrangement of auxiliary loads: in the lower part of guides 13.

After actuating the fan and the magnetron, the adapter 8 is set so thatthe energy reflected in guide 4 (measured by milliwattmeter 7) is at aminimum. One then obtains the following processing conditions: ##EQU1##Average energy density in the chamber: 0.06 cm³ /watts Ventilationair-flow: 100 liters/hour

Room temperature: 20° C.

Temperature on the inside surface of chamber wall: 30° C.

Processing time: 30 min.

At the end of processing, one obtains hyrophilic contact lenses,polymerized in uniform fashion, presenting no geometrical or opticaldefect and provided with perfectly formed thin edges. Each lens obtainedis apt to absorb about 38% of water (by weight in relation to finalweight of the hydrated lens).

EXAMPLE 2

This example aims toward a realization of very thin lenses having athickness on the order of 5/100 mm at the level of the optical axis.

Basic composition placed in each sealed mold:

    ______________________________________                                        Basic composition placed in each sealed mold:                                 ______________________________________                                        Vinyl Pyrrolidome N  74.58%                                                   Methyl methacrylate  24.84%                                                   Ethylene glycol dimethacrylate                                                                     0.50%                                                    Azobis iso butyro nitril                                                                           0.08%                                                    ______________________________________                                    

weight of portion within each mold: 0.040 g

Number of usable molds arranged in each chamber: 36

Clean weight of each mold: 0.85 g

Number of auxiliary loads formed by molds containing lost portions: 8

Arrangement of these auxiliary loads: in the lower part of guides 13.

One ascertains that the preceding setting of adapter 8 must be slightlymodified by reason of the modification in the composition placed in themolds. ##EQU2## Average energy density in the chamber: 0.025 cm³ /wattsVentilation air-flow: 100 liters/hour

Room temperature: 20° C.

Temperature on the inside surface of the chamber wall: 24° C.

Processing time: 90 min.

Despite their very slender thickness, one ascertains no deformities inthe lenses and, as presently, these latter possess the quality of beingfit for direct us (hydration rate: 70%).

EXAMPLE 3

    ______________________________________                                        Basic Composition:                                                                         2 hydroxy ethyl methacrylate                                                                     99.91%                                                     Azobis iso butyro nitril                                                                         0.09%                                         ______________________________________                                    

Weight of portion within each mold: 0.04 g

Number of usable molds arranged in the chambers: 56

Clean weight of each mold: 0.85 g

Number of auxiliary loads formed by molds containing lost portions: 16

Arrangement of auxiliary loads: in the lower part of guides 13 ##EQU3##Average energy density in the chamber: 0.045 cm³ /watts Ventilationair-flow: 100 liters/hour

Room temperature: 20° C.

Temperature on the inside surface of chamber wall: 25° C.

Processing time: 45 min.

Same remarks as previously may be made regarding the quality of lensesobtained (hydration rate: 40%).

EXAMPLE 4

In this example, the basic composition is identical to that in example1.

In tubular guide 28, five molds are superposed in a metrical fashionwith regard to the chamber center. These molds are of polymethylpentene.

Weight of the portion in each mold: 0.02 g

Clean weight of each mold: 1.18 g ##EQU4## Average energy density: 0.049cm³ /watts Processing time: 5 min.

At the end of this processing whose duration is very slight incomparison to the other examples, the lenses obtained are polymerized inuniform fashion, without geometrical or optical defect.

EXAMPLE 5

In this example, the basic composition, the portion weights and theweight and nature of the molds are identical to those of the preceedingexample.

The molds are made to pass continuously through a tubular guide 30 at aspeed on the order of 1 cm/min. (speed of conveyor 33). Each moldremains in the chamber about 30 min., the number of molds present in thechamber at each instant being about 14.

The energy absorbed/energy emitted yield and the average density are ofthe same order as those in the preceding example.

The same remarks may be made regarding the quality of lenses obtained.

We claim:
 1. A method of manufacturing a contact lens of appropriateoptical quality consisting of: constructing water-tight molds,reproducing, in the mold cavity, the shape of the lens desired andwherein said water-tight molds are composed of a substantiallytransparent material with respect to ultra high frequencyelectromagnetic waves, and said water-tight molds being constructed soas to possess a thermic inertia much higher than the portion of basiccomposition needed to make a lens;preparing a basic composition startingwith one or several monomers having double polymerizable bonds, andhaving an absorbent quality with respect to ultra high frequency waves;insuring polymerization of the composition within the sealed molds,through irradiation by means of ultra high frequency waves; said methodbeing characterized in that the polymerization operation is realized byarranging several molds (1), each containing an amount of basiccomposition, within at least one sealed metallic chamber (9)constituting a resonant cavity of a unique mode for the frequency of theultra high frequency waves used, said molds being positioned in an areaof the cavity where the electromagnetic field is approximatelyhomogeneous and being distributed so that the amounts of basiccomposition contained in said molds act as a load fitted to the insideof said resonant cavity.
 2. Method according to claim 1, characterizedin that the molds (1) are arranged in a chamber (9) possessing ringgeometry, constituting a resonant cavity according to TM 010 or TM 110modes, said chamber being excited so as to favor this mode of resonance.3. Method according to claim 2, characterized in that the molds (1) arearranged in chamber (9) excited by ultra high frequency radiation means(10, 25) fit to generate an electromagnetic field composed of anelectrical field whose lines of force are appreciably straight linesparallel to chamber's rotational axis, and of a magnetic field whoselines of force are curves located in planes perpendicular to thechamber's axis.
 4. Method according to claim 3, characterized in thatthe molds (1) are arranged in stacks, superposed upon one another toform at least one column situated the length of or around the chamber'srotational axis (9), said column(s) being positioned in a usable centralvolume of chamber representing a fraction of this latter's total volume.5. Method according to claim 4, characterized in that the molds areinserted in a resonant cavity according to the TM 010 mode and arearranged, on the one hand, as four stacks, called central columns, inthe immediate vicinity of a radiating antenna (10) extending the lengthof chamber's axis, and on the other hand, as four additional stacks,called peripheral columns, arranged at the immediate circumference ofthe central columns, each peripheral column being set in the spaceseparating the exterior circumference of the two neighboring centralcolumns.
 6. Method according to claim 5, characterized in that the molds(1) are arranged, on the one hand, as central columns in the immediatevicinity of the antenna (10) and extending almost the height of chamber(9), and on the other hand, as peripheral columns, arranged at theimmediate circumference of central columns and extending over a fractionof chamber's height.
 7. Method according to claim 4, characterized inthat the molds are inserted in a resonant cavity according to the TM 010mode excited by means of an iris (25), symmetrical in relation to thechamber's transverse median plane, said molds being arranged in atubular central guide (28, 30) running through chamber the length of itsaxis.
 8. Method according to claim 7, characterized in that the moldspass through central guide (30) at the appropriate speed so that eachmold remains in the chamber's usable central volume the necessary timefor processing.
 9. Method according to claim 6, characterized in thatone interposes in one of the columns of molds (1) auxiliary dielectricloads of an absorbent material with respect to ultra high frequencywaves, so as to increase the homogeneity of the electromagnetic field atmolds' level.
 10. Method according to claim 2, characterized in that oneinsures ventilation a cooling of the upper portion of the chamber, tomake the temperature homogeneous within this latter and to insure, atthe level of the molds, a temperature lower than approximately 40° C.11. Method according to claim 3, characterized in that chamber (9) issupplied with ultra high frequency waves so that the average energydensity within this latter may be comprised between approximately 10⁻²and 50×10⁻² cm³ /watts.
 12. Method according to claim 1, in which thebasic composition is a monomer or a mixture of monomers, having a highvolume molecule, from the following group: hydrox ethyl methacrylate,hydroxy propyl methacrylate, hydroxy ethyl acrylate, ethylene glycoldimethacrylate, vinyl pyrrolidone N, methyl methacrylate, methacrylicacid characterized in that one mixes with said basic composition aninitiator made in particular of azobis iso butyro nitril, or ahydro-peroxide or a peroxide, in weight proportion comprised betweenapproximately 0.04% and 0.15%.